state of matter into which gases and liquids are converted at elevated temperature and high pressure; supercritical fluid has characteristic of both liquid and a gas; it lacks any surface tension while interacting with solid surfaces, and hence, can readily penetrates high aspect ratio geometrical features; it has very low viscosity and, like a liquid, easily dissolves large quantities of other chemicals; in semiconductor processing used in surface cleaning when penetration of very tight geometrical features is required; typically supercritical CO2 is used as carrier of cleaning agents.